<pre>  /**
   * The constants used in this Content Widget.
   */
  public static interface CwConstants extends Constants {
    String[] cwListBoxCars();

    String[] cwListBoxCategories();

    String cwListBoxDescription();

    String cwListBoxName();

    String cwListBoxSelectAll();

    String cwListBoxSelectCategory();

    String[] cwListBoxSports();

    String[] cwListBoxVacations();
  }

  /**
   * An instance of the constants.
   */
  private final CwConstants constants;

  /**
   * Initialize this example.
   */
  @Override
  public Widget onInitialize() {
    // Create a panel to align the Widgets
    HorizontalPanel hPanel = new HorizontalPanel();
    hPanel.setSpacing(20);

    // Add a drop box with the list types
    final ListBox dropBox = new ListBox(false);
    String[] listTypes = constants.cwListBoxCategories();
    for (int i = 0; i &lt; listTypes.length; i++) {
      dropBox.addItem(listTypes[i]);
    }
    dropBox.ensureDebugId("cwListBox-dropBox");
    VerticalPanel dropBoxPanel = new VerticalPanel();
    dropBoxPanel.setSpacing(4);
    dropBoxPanel.add(new HTML(constants.cwListBoxSelectCategory()));
    dropBoxPanel.add(dropBox);
    hPanel.add(dropBoxPanel);

    // Add a list box with multiple selection enabled
    final ListBox multiBox = new ListBox(true);
    multiBox.ensureDebugId("cwListBox-multiBox");
    multiBox.setWidth("11em");
    multiBox.setVisibleItemCount(10);
    VerticalPanel multiBoxPanel = new VerticalPanel();
    multiBoxPanel.setSpacing(4);
    multiBoxPanel.add(new HTML(constants.cwListBoxSelectAll()));
    multiBoxPanel.add(multiBox);
    hPanel.add(multiBoxPanel);

    // Add a handler to handle drop box events
    dropBox.addChangeHandler(new ChangeHandler() {
      public void onChange(ChangeEvent event) {
        showCategory(multiBox, dropBox.getSelectedIndex());
        multiBox.ensureDebugId("cwListBox-multiBox");
      }
    });

    // Show default category
    showCategory(multiBox, 0);
    multiBox.ensureDebugId("cwListBox-multiBox");

    // Return the panel
    return hPanel;
  }

  /**
   * Display the options for a given category in the list box.
   *
   * @param listBox the ListBox to add the options to
   * @param category the category index
   */
  private void showCategory(ListBox listBox, int category) {
    listBox.clear();
    String[] listData = null;
    switch (category) {
      case 0:
        listData = constants.cwListBoxCars();
        break;
      case 1:
        listData = constants.cwListBoxSports();
        break;
      case 2:
        listData = constants.cwListBoxVacations();
        break;
    }
    for (int i = 0; i &lt; listData.length; i++) {
      listBox.addItem(listData[i]);
    }
  }

</pre>